This invention relates to a displacement magnifying mechanism for a print element. More particularly, this invention relates to a displacement magnifying mechanism having a piezo-electric element for driving a print element.
In recent years, a printer is required to realize a high speed printing operation. In order to attain such an objective, a piezo-electric element is used for the driving source of the print element. In addition, a highly efficient displacement magnifying mechanism is necessary to realize yet a higher speed printing operation.
FIG. 1 is a perspective view of a conventional print element having a displacement magnifying mechanism. FIG. 2 is a perspective view of a conventional connection part for the print element of FIG. 1. FIG. 3 is a further perspective view of a conventional connection part for the print element of FIG. 1.
The conventional print element comprises a fixing member 6 and a piezo-electric element 5 operable in a longitudinal mode. The fixing member 6 has opposite side portions 6a, 6b and a bottom portion 6c so that member 6 has a U-shaped configuration. The piezo-electric element 5 is disposed between the opposite portions 6a, 6b. The piezo-electric element 5 has a base end 5a and a free end 5b. The base end 5a is fixed to the bottom portion 6c of the fixing member 6. The element axis passes through the base end and the free end.
It should be understood that the piezo-electric element 5 is depicted in FIG. 1 in a rest state, wherein no voltage is supplied across the piezo-electric element 5. When a voltage is supplied across the piezo-electric element 5, the piezo-electric element 5 is put in an actuated state to extend so that the free end 5b moves away from the base end 5a along the element axis. When the voltage is removed, the piezo-electric element 5 contracts along the element axis to return to the rest state. In summary, the piezo-electric element 5 has rest and actuates states, in which the piezo-electric element 5 extends and contracts along the element axis to give a displacement to the free end relative to the base end.
The print element also includes an arm 1 with a first end and a second end, the first end of the arm 1 having an arm base 1a and the second end of arm 1 having a print wire 8. A first resilient hinge 2 has first and second ends. The first end of the first resilient hinge 2 is connected to the free end 5b of the piezo-electric element 5 through a junction member 7. The second end of the resilient hinge 2 is connected to the arm base 1a. A second resilient hinge 3 has first and second ends. The first end of the second resilient hinge 3 is connected to the side portion 6a of the fixing member 6. The second end of the second resilient hinge 3 is connected to the arm base 1a. A third resilient hinge 4 has first and second ends. The first end of the third first resilient hinge 4 is connected to the side portion 6b of the fixing member 6. The second end of third resilient hinge 3 is connected to the arm base 1a.
When a voltage is supplied across the piezo-electric element 5 (actuate state), the piezo-electric element 5 moves the junction member 7 a predetermined amount in the direction of the arrow "A" shown in FIG. 1, thereby applying a compression force on the first resilient hinge 2. As a result, the end of the arm 1 moves in the direction of the arrow mark "B" shown in FIG. 1 due to the elastic effect of the hinges 2, 3 and 4. In this case, a sufficient magnifying displacement mechanism is applied to the print head, the print wire 8 being activated when the arm 1 moves. When the voltage is removed at a predetermined period, the piezo-electric element 5 contracts along the element axis to return to the rest state, that is, its initial position. Similarly, the hinges 2, 3 and 4 return to their initial positions. In this case, since extension and contraction of piezo-electric element 5 are carried out quickly, high speed printing can be realized by applying this displacement magnifying mechanism to the print head.
This type of printer arrangement is further disclosed in European Patent Publication (A1) No. 0 285 766, published on Dec. 10, 1988.
Improvement in displacement magnifying efficiency of this print head would require a smaller interval between the parallel first resilient hinge 2 and second and third resilient hinges 3, 4. However, if this was attempted, the second and third resilient hinges 3, 4 connected to side portions 6a, 6b of the fixing member and junction member 7 would collide with each other. Therefore, the conventional print head has resulted in a bad mounting efficiency because the second and third hinges 3, 4 are provided on both sides of the first hinge such as to avoid the first hinge 2 and piezo-electric element 5, thereby requiring a larger width for the mechanism.